(1) Field of the Invention
This invention relates to an integrated process for the production of methanol and ammonia from a gaseous hydrocarbon feed.
(2) Description of the Prior Art
The combined production of methanol and ammonia from a hydrocarbon feed is well known as is disclosed in U.S. Pat. No. 3,598,527. According to the process of this U.S. Patent, natural gas is subjected to primary reforming with steam and to secondary reforming with steam and an oxygen-containing gas, so that a methanol synthesis gas containing hydrogen, carbon monoxide and nitrogen is produced. This methanol synthesis gas is then subjected to low pressure methanol synthesis. The effluent stream from this methanol synthesis step is separated into crude methanol and a purge gas. While the crude methanol is purified to obtain product methanol, the purge gas is subjected to high temperature and low temperature water-gas shift conversion whereby the carbon monoxide contained therein is converted into hydrogen and carbon dioxide. The gas resulting from this water-gas shift conversion step is freed of carbon oxides to a substantially complete degree by passing it through carbon dioxide removal and methanation steps, compressed to a desired ammonia synthesis pressure, and then subjected to ammonia synthesis.
When compared with the separate production of methanol and ammonia, the above-described process has several advantages such as lowered capital investment and reduced operating costs. However, it still remains to be improved in some respects. More specifically, since a methanol synthesis gas is produced by both primary reforming and secondary reforming, it contains nitrogen which is unnecessary for methanol synthesis. This lowers the effective pressure for methanol synthesis. Moreover, it is required to increase the capacities of the methanol synthesis tube, methanol synthesis gas compressor and circulating gas pump in proportion to the nitrogen content. Furthermore, during methanol synthesis, the nitrogen present in the methanol synthesis gas tends to form methylamines as impurities, thus leading to a complicated procedure for the purification of crude methanol.